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Recognize bounded MIPS switches with scheduled table constants

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This commit is contained in:
Matthew Stanley
2026-09-11 13:38:06 -07:00
parent 6f77dcc31f
commit fe2c0046ba
7 changed files with 281 additions and 27 deletions
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recompiler/src/function_analysis.cpp
+39 -12
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@@ -894,16 +894,36 @@ bool resolve_exact_bounded_jump_table(
return false;
}
// Exact canonical guard: sltiu; beq; nop; sll. This is the same accepted
// suffix as the Python capture verifier and excludes unrelated bounds.
// Exact guards: sltiu; beq; nop; sll, or sltiu; beq; lui; addiu; sll.
// The latter schedules the table's LUI in the bounds branch's delay slot.
// Keep both forms in parity with the Python capture verifier.
if (sll_pc < entry + 12u) return false;
uint32_t guard_pc = sll_pc - 8u;
uint32_t bound_pc = sll_pc - 12u;
auto before_scale = read(sll_pc - 4u);
if (!before_scale.has_value()) return false;
bool scheduled_base = *before_scale != 0u;
if (scheduled_base) {
// R3000 JR would see the old target register without this load delay.
if (lw_pc != jr_pc - 8u) return false;
if (sll_pc < entry + 16u) return false;
guard_pc -= 4u;
bound_pc -= 4u;
auto upper_word = read(sll_pc - 8u);
if (!upper_word.has_value()) return false;
uint32_t upper_reg = (*upper_word >> 16) & 0x1Fu;
if ((*upper_word >> 26) != 0x0Fu ||
((*upper_word >> 21) & 0x1Fu) != 0u || upper_reg == 0u ||
(*before_scale >> 26) != 0x09u ||
((*before_scale >> 21) & 0x1Fu) != upper_reg ||
((*before_scale >> 16) & 0x1Fu) != base_reg ||
upper_reg == index_reg || base_reg == index_reg) {
return false;
}
}
auto guard_word_opt = read(guard_pc);
auto bound_word = read(bound_pc);
auto guard_delay = read(sll_pc - 4u);
if (!guard_word_opt.has_value() || !bound_word.has_value() ||
!guard_delay.has_value() || *guard_delay != 0u) {
if (!guard_word_opt.has_value() || !bound_word.has_value()) {
return false;
}
uint32_t guard_word = *guard_word_opt;
@@ -920,20 +940,23 @@ bool resolve_exact_bounded_jump_table(
uint32_t bound_rt = (*bound_word >> 16) & 0x1Fu;
uint32_t count = *bound_word & 0xFFFFu;
if (bound_op != 0x0Bu || bound_rs != index_reg ||
bound_rt != bound_reg || count == 0u || count >= 512u ||
bound_rt != bound_reg || bound_reg == index_reg ||
count == 0u || count >= 512u ||
in_delay_slot(bound_pc)) {
return false;
}
uint32_t guard_target = exact_branch_target(guard_pc, guard_word);
if ((guard_target & 3u) != 0u || guard_target < entry ||
guard_target >= hard_cap ||
(guard_target >= sll_pc && guard_target < jr_pc + 8u)) {
(guard_target >= sll_pc && guard_target < jr_pc + 8u) ||
(scheduled_base && guard_target > bound_pc && guard_target < jr_pc + 8u)) {
return false;
}
// Resolve the table-base reaching definition. Cross-register constants
// (`lui rA; addiu rB,rA,lo`) are valid, but both definitions must be local,
// unskippable, outside delay slots, and unclobbered before use.
// unskippable and unclobbered before use. Only the validated scheduled
// form permits LUI in a delay slot, exactly that of the bounds BEQ.
uint32_t low_pc = 0, source_reg = base_reg;
int16_t low = 0;
uint32_t lui_pc = 0, upper = 0;
@@ -974,7 +997,9 @@ bool resolve_exact_bounded_jump_table(
break;
}
}
if (lui_pc == 0u || in_delay_slot(lui_pc) ||
if (scheduled_base && (lui_pc != guard_pc + 4u || low_pc != sll_pc - 4u))
return false;
if (lui_pc == 0u || (in_delay_slot(lui_pc) && !scheduled_base) ||
(low_pc != 0u && in_delay_slot(low_pc)) ||
inbound_skips(lui_pc, addu_pc) ||
(low_pc != 0u && inbound_skips(low_pc, addu_pc)) ||
@@ -1026,6 +1051,7 @@ bool resolve_exact_bounded_jump_table(
uint32_t runtime_target = *target_word;
uint32_t image_target = mapped(runtime_target);
if (image_target < entry || image_target >= hard_cap ||
(scheduled_base && image_target > bound_pc && image_target < jr_pc + 8u) ||
image_target < producer_lo || image_target >= producer_hi ||
(image_target & 3u) != 0u) {
return false;
@@ -1089,6 +1115,7 @@ bool resolve_exact_bounded_jump_table(
break;
}
}
uint32_t protected_pc = scheduled_base ? bound_pc : lui_pc;
for (uint32_t source = entry; source < hard_cap; source += 4u) {
auto word = read(source);
if (!word.has_value()) return false;
@@ -1096,9 +1123,9 @@ bool resolve_exact_bounded_jump_table(
bool direct = cf.kind == ExactCfKind::Branch ||
cf.kind == ExactCfKind::Jump ||
cf.kind == ExactCfKind::Jal;
if (direct && cf.target > lui_pc && cf.target <= jr_pc &&
(source < lui_pc || source > jr_pc) &&
!case_reachable.count(source)) {
if (direct && cf.target > protected_pc && cf.target <= jr_pc &&
(source < protected_pc || source > jr_pc) &&
(scheduled_base || !case_reachable.count(source))) {
return false;
}
}